1. Field of the Invention
The present invention relates to an orifice plate itself, defining a plurality of orifices or a liquid jet unit which is integrally provided with the orifice plate and a recording apparatus using the liquid jet unit. The present invention particularly but not exclusively relates to an ink jet head and an ink jet apparatus. In the ink jet head and the ink jet system, an orifice defining member which defines ink orifices is integrally formed with a top or a cap plate for forming liquid passages and a common liquid chamber.
2. Description of the Prior Art
Heretofore, liquid jet systems have bene used in various fields, and among them liquid jet systems for recording have been placed into the market. In the typical conventional methods of forming liquid droplets, there is a bubble forming method by thermal energy which is disclosed in U.S. Pat. Nos. 4,723,129 and 4,740,796. This method is capable of appropriately ejecting droplets in response to recording signals and is hence effective. In another attempt, a piezoelectric transducer was used.
The orifices taught in these publications are formed at a high density and usually have circular cross-sections. The patents disclose that machining is conducted by using a laser for efficiently forming the orifices. In the recording head fabricating methods of these patents, several members, one of which is a grooved plate, are bonded to form orifices at one of the laminated edges or an orifice plate is used to form many orifices. Such a laminated recording head is clearly shown and described in U.S. Pat. No. 4,678,529, in which the orifices and liquid passages communicating to the orifices are formed to have triangular cross-sections.
Conventionally, it was understood that it is optional whether orifices have polygonal or circular cross-sections. Moreover, little attempt was made to pay attention to the cross-sectional shape of the liquid passages. One such attempt is disclosed in U.S. Pat. No. 4,752,787. The known publications teach that orifices are formed at a high density but in practice any recording head which has liquid jet orifices capable of recording at more than 360 dpi has not yet been realized.
In several U.S. applications which have been assigned to Canon Kabushiki Kaisha, the Assignee of the subject application, in view of the prior art the following proposals have been made to effectively provide high density arrangement orifices. 1. An orifice plate and a grooved member for defining liquid passages are molded in one piece. The orifice plate and a substrate are mated in the vicinity of the orifices without using any adhesive. This invention is disclosed in U.S. Ser. No. 07/583,336. The invention is advantageous in that: there is no possibility that the orifice area is changed in shape by an adhesive entering in the orifice area; and the fabrication dispersion of the head is reduced. In addition to the features of the invention, U.S. Ser. No. 07/583,238 teaches that tapering is provided to the common liquid chamber in three directions. 2. A resilient urging member which is arranged to provide pressure in a direction of the arrangement of the orifices to stabilize contact of the mating is disclosed in U.S. Ser. NO. 07/583,168. This urging member holds the orifice area in a stable condition. 3. Grooves which define liquid feed passages are formed to have an equal leg trapezoidal cross-section, and the orifices are formed by a focus-type excimer laser using the grooves for enhancing machining accuracy. This invention is disclosed in U.S. Ser. No. 07/583,335. This laser machining is advantageous in that: each orifice can be formed with a minimum cross-sectional area by forming it from the side of the corresponding liquid passage; and the orifices may be formed in an equal leg trapezoidal cross-section.
These inventions may be effectively applied to the present invention as will be understood from embodiments of the present invention described hereinafter.
Although liquid passages may be polygonal or circular in cross-section, it has been found that orifices preferably have polygonal sides rather than a circular cross-section for improving ejection efficiency of an orifice plate which defines the orifices. This fact is significant for high density orifice arrangement. The inventors have conducted durability tests in which high density orifices of a polygonal cross-section underwent changes in various environmental conditions.
It was however found that during the tests cracks 40 as shown in FIG. 10 were produced before the end of the life of discharging elements, that is, the end of the life of heads. These cracks were produced from the front side of the orifice plate but the reason for the production of the cracks was not clear. It was considered that the cracks were peculiarly produced. Further study revealed that the more complicated the duration test became the more cracks were produced. Such a test included rapid temperature changes and excessive continuous ejection in low temperature environments. Cracks were found in part of heads either. These heads had undergone a drop test after a duration test which had produced no significant cracks, or had been subjected to a duration test after a drop test which had provided no problem as to cracks. Heretofore, no attention was paid to these phenomena. The inventors have studied causes of this problem, and thereby have completed the present invention which solves the problem.